Endbearing on rock with particular reference to sandstone

This paper briefly reviews end bearing loading of rock from the theoretical viewpoint and then presents the results of laboratory and field tests on sandstone. Theoretical analysis suggests that due to the brittleness of rock the ultimate bearing capacity should be considerably less than that of a plastic material of the same shear strength. This is supported by the results of model bearing capacity tests which also show that ultimate bearing capacity of intact sandstone is only mobilized at very large displacements (of the order of 20 per cent of the footing diameter). Theoretical methods for evaluating the effects of joints on bearing capacity behaviour are very limited but in such a confined problem it appears that tight joints do not cause a major reduction in the ultimate bearing capacity. However, in the field joints are associated with differential weakening of the rock material and are often clay filled. The end bearing behaviour of such fractured, non uniform rock can only be determined on the basis of field tests. A number of such field tests conducted on different classes of hawkesbury sandstone have shown that in most cases the allowable bearing pressure will be dictated by the displacements that may be acceptable for a particular structure. Such allowable pressures may be estimated from the bearing pressure versus displacement curves presented in this paper.